Batteries are commonly used as power supplies in electric devices, such as electric vehicles and various kinds of portable electric equipments. FIG. 1 is a block diagram illustrating a conventional battery charging circuit 100. The charging circuit 100 includes a charger 102 for charging a battery pack 104 which includes multiple battery cells 106. The charger 102 includes a positive terminal CH+ and a negative terminal CH− for providing power to charge the battery pack 104. The battery pack 104 includes a positive terminal BAT+ and a negative terminal BAT− for receiving power from the charger.
Due to a misuse of an inappropriate charger to charge a battery, the battery may be damaged. For example, if the charger 102 provides a 64V output voltage while the maximum allowable charging voltage of the battery pack 104 is 48V, the battery pack 104 may be damaged. On the other hand, if the charger 102 becomes over-heated during charging due to circuit failure or poor ventilation, the charger 102 may also be damaged. Therefore, there exists a need to provide an improved charging circuit that the user can be warned if an inappropriate charger is used to charge the battery or if the circuit becomes over-heated.